1. (Field of the Invention)
The present invention relates to a dental soft relining material of the type of a silicon rubber used on the mucosa surface of a resin denture base, to a denture, and to a method of repairing the denture.
2. (Prior Art)
Patients who need a denture and, particularly, a full denture, in many cases, are aged persons, and their alveolar ridges must bear an increased occlusion force per a unit area since the bone has generally been resorbed to a conspicuous degree. The mucosa of alveolar ridge becomes thin due to senile atrophy, and the occlusion stress or masticatory pressure is not softened but is directly transmitted to the alveolar bone. Moreover, a thin mucosa disposed between a hard resin denture base and the hard alveolar bone is tightened and gets hurt after every occlusion, and begins to feel pain.
In such a serious case, the resin denture base molded by using a methyl methacrylate resin that is usually used is not sufficient for stably maintaining and supporting the denture. It is necessary to reline the mucosa surface of the resin denture base with a soft dental relining material to compensate the lost viscoelasticity of the mucosa of the residual alveolar ridge, in order to impart cushioning property that softens the occlusal stress. That is, the object of reining with a soft material is to overcome various troubles that develop when the mucosa below denture is compressed by the hard denture base.
Dental soft relining materials used, so far, for the clinic include a (meth)acrylic acid ester polymer, a fluorine-contained resin, a polyolefin type resin, a silicone rubber, and the like. For temporary applications, furthermore, there is used a denture adhesive (so-called false tooth adhesive). As for the denture adhesive, the consistency increases as it is used for extended periods of time and the plasticity decreases. As a result, the fit and marginal shut of ill-fitting denture are not improved and, hence, the object of enhancing the stability and support of the denture base is not fully accomplished and, besides, the oral tissue is damaged in many cases. Moreover, since the denture has a small compressive stress and lacks elasticity, its cushioning effect is not sufficient for the occlusal stress and that becomes a cause of the recurrence of pain in the oral mucosa.
The soft material such as the (meth)acrylic acid polymer or the like lacks chemical stability in the oral cavity, becomes hard and brittle within several months, and are not usable for extended periods of time. The fluorine-contained relining material lacks viscoelasticity from which sufficient cushioning effect cannot be expected. The polyolefin type relining material has many problems from a practical point of view. That is, it may deform the resin denture base because the preparation temperature is high, and it requires a plurality of adhesives and a special heating device, involving a cumbersome operation. The silicone rubber-type relining material is relatively stable. However, the conventional relining materials of the condensed type or of the heated silicone rubber-type get colored and are not satisfactory in regard to durability and operability, since they cannot be trimmed. As a method of solving these problems inherent in the relining material of the silicone rubber type, therefore, we have proposed a relining material of the addition-type silicone rubber (U.S. Pat. No. 5,513,987, Japanese Laid-Open Patent Publication No. 41411/1995). However, this soft relining material is not still satisfactory from the relation of the strength and the resistance against being colored. That is, when a fine powdery silica such as fumed silica is added at a large ratio to further increase the strength of the silicone rubber, the cured product exhibits an increased strength but is, at the same time, colored to a large extent, and does not necessarily exhibit satisfactory properties for use as a soft relining material. The reason is because, the soft relining material is used for more than a year and often several years in an environment of oral cavity. It cannot be said that the relining material offers a satisfactory function if it breaks, cracks or is conspicuously contaminated upon absorbing oils in the foods or saliva during the use. That is, the former one is related to a form involving trouble in the function, and the latter one is related to a problem of environment in which it is used, such as offensive odor, appearance, etc. It is therefore demanded to further increase the strength and resistance against being colored.
As described above, the dental soft relining material for denture base provided so far loses physical properties after the use of a short period of time, can be used in the oral cavity for only a short period of time, cannot offer satisfactory cushioning effect, can be used requiring cumbersome method, and is not practicable. Among them, even the soft relining material of the addition-type silicone rubber that had been thought to be capable of enduring the clinical use, is not satisfactory from the relation of both the strength and the resistance against being colored. It has therefore been desired to provide a soft relining material for dental use having a suitable viscoelasticity and a sufficient degree of strength and a resistance against being colored. In particular, the soft relining material for dental use having such properties is strongly demanded toward the coming aging society.